Multi-frequency broadband piezoelectric micromachined ultrasonic transducer utilizing helmholtz resonance

Piezoelectric micromachined ultrasonic transducers (PMUTs) with multi-frequency are appealing for ultrasonic applications, which can meet the requirements of large detection depth and high resolution simultaneously. Hence, a novel structure with series Helmholtz resonators under the PMUT membrane term as dual-cavity serial PMUT is presented, which utilizes both the piezoelectric effect and Helmholtz resonant effect to achieve multifrequency and further widens the bandwidth. Based on the mechanism of vibration coupling between the membrane and Helmholtz resonator, a lumped model and an equivalent circuit model are formulated. Meanwhile, the finite element method (FEM) is developed to investigate the multi-resonance and make comprehensive validations. The results demonstrate that the multi-frequency is contributed by the induced acoustic impedance of the Helmholtz resonator, causing a simulated average sound pressure of up to 260 Pa/V at the resonance frequency and a 77% -6 dB frequency bandwidth in air by theoretical analysis and parameter optimization. The proposed dual-cavity serial PMUT provides a new approach for the application of high transmission power and broad bandwidth transducers.